Merge pull request #1927 from robertwb/multi-inheritance

Multiple inheritance

CHANGES.rst

@@ -8,6 +8,10 @@ Cython Changelog
 Features added
 --------------
 
+* Cdef classes can now multiply inherit from ordinary Python classes.
+  (The primary base must still be a c class, possibly ``object``, and
+  the other bases must *not* be cdef classes.)
+
 * Type inference is now supported for Pythran compiled NumPy expressions.
   Patch by Nils Braun.  (Github issue #1954)
 

Cython/Compiler/ModuleNode.py

@@ -2948,8 +2948,8 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
             else:
                 self.generate_base_type_import_code(env, entry, code)
                 self.generate_exttype_vtable_init_code(entry, code)
-                self.generate_type_ready_code(env, entry, code)
-                self.generate_typeptr_assignment_code(entry, code)
+                if entry.type.early_init:
+                    self.generate_type_ready_code(entry, code)
 
     def generate_base_type_import_code(self, env, entry, code):
         base_type = entry.type.base_type
@@ -3023,98 +3023,8 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
             not type.is_external or type.is_subclassed,
             error_code))
 
-    def generate_type_ready_code(self, env, entry, code):
-        # Generate a call to PyType_Ready for an extension
-        # type defined in this module.
-        type = entry.type
-        typeobj_cname = type.typeobj_cname
-        scope = type.scope
-        if scope: # could be None if there was an error
-            if entry.visibility != 'extern':
-                for slot in TypeSlots.slot_table:
-                    slot.generate_dynamic_init_code(scope, code)
-                code.putln(
-                    "if (PyType_Ready(&%s) < 0) %s" % (
-                        typeobj_cname,
-                        code.error_goto(entry.pos)))
-                # Don't inherit tp_print from builtin types, restoring the
-                # behavior of using tp_repr or tp_str instead.
-                code.putln("%s.tp_print = 0;" % typeobj_cname)
-                # Fix special method docstrings. This is a bit of a hack, but
-                # unless we let PyType_Ready create the slot wrappers we have
-                # a significant performance hit. (See trac #561.)
-                for func in entry.type.scope.pyfunc_entries:
-                    is_buffer = func.name in ('__getbuffer__', '__releasebuffer__')
-                    if (func.is_special and Options.docstrings and
-                            func.wrapperbase_cname and not is_buffer):
-                        slot = TypeSlots.method_name_to_slot[func.name]
-                        preprocessor_guard = slot.preprocessor_guard_code()
-                        if preprocessor_guard:
-                            code.putln(preprocessor_guard)
-                        code.putln('#if CYTHON_COMPILING_IN_CPYTHON')
-                        code.putln("{")
-                        code.putln(
-                            'PyObject *wrapper = PyObject_GetAttrString((PyObject *)&%s, "%s"); %s' % (
-                                typeobj_cname,
-                                func.name,
-                                code.error_goto_if_null('wrapper', entry.pos)))
-                        code.putln(
-                            "if (Py_TYPE(wrapper) == &PyWrapperDescr_Type) {")
-                        code.putln(
-                            "%s = *((PyWrapperDescrObject *)wrapper)->d_base;" % (
-                                func.wrapperbase_cname))
-                        code.putln(
-                            "%s.doc = %s;" % (func.wrapperbase_cname, func.doc_cname))
-                        code.putln(
-                            "((PyWrapperDescrObject *)wrapper)->d_base = &%s;" % (
-                                func.wrapperbase_cname))
-                        code.putln("}")
-                        code.putln("}")
-                        code.putln('#endif')
-                        if preprocessor_guard:
-                            code.putln('#endif')
-                if type.vtable_cname:
-                    code.putln(
-                        "if (__Pyx_SetVtable(%s.tp_dict, %s) < 0) %s" % (
-                            typeobj_cname,
-                            type.vtabptr_cname,
-                            code.error_goto(entry.pos)))
-                    code.globalstate.use_utility_code(
-                        UtilityCode.load_cached('SetVTable', 'ImportExport.c'))
-                if not type.scope.is_internal and not type.scope.directives['internal']:
-                    # scope.is_internal is set for types defined by
-                    # Cython (such as closures), the 'internal'
-                    # directive is set by users
-                    code.putln(
-                        'if (PyObject_SetAttrString(%s, "%s", (PyObject *)&%s) < 0) %s' % (
-                            Naming.module_cname,
-                            scope.class_name,
-                            typeobj_cname,
-                            code.error_goto(entry.pos)))
-                weakref_entry = scope.lookup_here("__weakref__") if not scope.is_closure_class_scope else None
-                if weakref_entry:
-                    if weakref_entry.type is py_object_type:
-                        tp_weaklistoffset = "%s.tp_weaklistoffset" % typeobj_cname
-                        if type.typedef_flag:
-                            objstruct = type.objstruct_cname
-                        else:
-                            objstruct = "struct %s" % type.objstruct_cname
-                        code.putln("if (%s == 0) %s = offsetof(%s, %s);" % (
-                            tp_weaklistoffset,
-                            tp_weaklistoffset,
-                            objstruct,
-                            weakref_entry.cname))
-                    else:
-                        error(weakref_entry.pos, "__weakref__ slot must be of type 'object'")
-                if scope.lookup_here("__reduce_cython__") if not scope.is_closure_class_scope else None:
-                    # Unfortunately, we cannot reliably detect whether a
-                    # superclass defined __reduce__ at compile time, so we must
-                    # do so at runtime.
-                    code.globalstate.use_utility_code(
-                        UtilityCode.load_cached('SetupReduce', 'ExtensionTypes.c'))
-                    code.putln('if (__Pyx_setup_reduce((PyObject*)&%s) < 0) %s' % (
-                                  typeobj_cname,
-                                  code.error_goto(entry.pos)))
+    def generate_type_ready_code(self, entry, code):
+        Nodes.CClassDefNode.generate_type_ready_code(entry, code)
 
     def generate_exttype_vtable_init_code(self, entry, code):
         # Generate code to initialise the C method table of an
@@ -3145,15 +3055,6 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
                             cast,
                             meth_entry.func_cname))
 
-    def generate_typeptr_assignment_code(self, entry, code):
-        # Generate code to initialise the typeptr of an extension
-        # type defined in this module to point to its type object.
-        type = entry.type
-        if type.typeobj_cname:
-            code.putln(
-                "%s = &%s;" % (
-                    type.typeptr_cname, type.typeobj_cname))
-
 def generate_cfunction_declaration(entry, env, code, definition):
     from_cy_utility = entry.used and entry.utility_code_definition
     if entry.used and entry.inline_func_in_pxd or (not entry.in_cinclude and (

Cython/Compiler/Nodes.py

@@ -4453,36 +4453,13 @@ class PyClassDefNode(ClassDefNode):
         if self.is_py3_style_class:
             error(self.classobj.pos, "Python3 style class could not be represented as C class")
             return
-        bases = self.classobj.bases.args
-        if len(bases) == 0:
-            base_class_name = None
-            base_class_module = None
-        elif len(bases) == 1:
-            base = bases[0]
-            path = []
-            from .ExprNodes import AttributeNode, NameNode
-            while isinstance(base, AttributeNode):
-                path.insert(0, base.attribute)
-                base = base.obj
-            if isinstance(base, NameNode):
-                path.insert(0, base.name)
-                base_class_name = path[-1]
-                if len(path) > 1:
-                    base_class_module = u'.'.join(path[:-1])
-                else:
-                    base_class_module = None
-            else:
-                error(self.classobj.bases.args.pos, "Invalid base class")
-        else:
-            error(self.classobj.bases.args.pos, "C class may only have one base class")
-            return None
 
+        from . import ExprNodes
         return CClassDefNode(self.pos,
                              visibility='private',
                              module_name=None,
                              class_name=self.name,
-                             base_class_module=base_class_module,
-                             base_class_name=base_class_name,
+                             bases=self.classobj.bases or ExprNodes.TupleNode(self.pos, args=[]),
                              decorators=self.decorators,
                              body=self.body,
                              in_pxd=False,
@@ -4574,8 +4551,7 @@ class CClassDefNode(ClassDefNode):
     #  module_name        string or None    For import of extern type objects
     #  class_name         string            Unqualified name of class
     #  as_name            string or None    Name to declare as in this scope
-    #  base_class_module  string or None    Module containing the base class
-    #  base_class_name    string or None    Name of the base class
+    #  bases              TupleNode         Base class(es)
     #  objstruct_name     string or None    Specified C name of object struct
     #  typeobj_name       string or None    Specified C name of type object
     #  in_pxd             boolean           Is in a .pxd file
@@ -4655,44 +4631,34 @@ class CClassDefNode(ClassDefNode):
                 self.module.has_extern_class = 1
                 env.add_imported_module(self.module)
 
-        if self.base_class_name:
-            if self.base_class_module:
-                base_class_scope = env.find_imported_module(self.base_class_module.split('.'), self.pos)
-                if not base_class_scope:
-                    error(self.pos, "'%s' is not a cimported module" % self.base_class_module)
-                    return
+        if self.bases.args:
+            base = self.bases.args[0]
+            base_type = base.analyse_as_type(env)
+            if base_type in (PyrexTypes.c_int_type, PyrexTypes.c_long_type, PyrexTypes.c_float_type):
+                # Use the Python rather than C variant of these types.
+                base_type = env.lookup(base_type.sign_and_name()).type
+            if base_type is None:
+                error(base.pos, "First base of '%s' is not an extension type" % self.class_name)
+            elif base_type == PyrexTypes.py_object_type:
+                base_class_scope = None
+            elif not base_type.is_extension_type and \
+                     not (base_type.is_builtin_type and base_type.objstruct_cname):
+                error(base.pos, "'%s' is not an extension type" % base_type)
+            elif not base_type.is_complete():
+                error(base.pos, "Base class '%s' of type '%s' is incomplete" % (
+                    base_type.name, self.class_name))
+            elif base_type.scope and base_type.scope.directives and \
+                     base_type.is_final_type:
+                error(base.pos, "Base class '%s' of type '%s' is final" % (
+                    base_type, self.class_name))
+            elif base_type.is_builtin_type and \
+                     base_type.name in ('tuple', 'str', 'bytes'):
+                error(base.pos, "inheritance from PyVarObject types like '%s' is not currently supported"
+                      % base_type.name)
             else:
-                base_class_scope = env
-            if self.base_class_name == 'object':
-                # extension classes are special and don't need to inherit from object
-                if base_class_scope is None or base_class_scope.lookup('object') is None:
-                    self.base_class_name = None
-                    self.base_class_module = None
-                    base_class_scope = None
-            if base_class_scope:
-                base_class_entry = base_class_scope.find(self.base_class_name, self.pos)
-                if base_class_entry:
-                    if not base_class_entry.is_type:
-                        error(self.pos, "'%s' is not a type name" % self.base_class_name)
-                    elif not base_class_entry.type.is_extension_type and \
-                             not (base_class_entry.type.is_builtin_type and
-                                  base_class_entry.type.objstruct_cname):
-                        error(self.pos, "'%s' is not an extension type" % self.base_class_name)
-                    elif not base_class_entry.type.is_complete():
-                        error(self.pos, "Base class '%s' of type '%s' is incomplete" % (
-                            self.base_class_name, self.class_name))
-                    elif base_class_entry.type.scope and base_class_entry.type.scope.directives and \
-                             base_class_entry.type.is_final_type:
-                        error(self.pos, "Base class '%s' of type '%s' is final" % (
-                            self.base_class_name, self.class_name))
-                    elif base_class_entry.type.is_builtin_type and \
-                             base_class_entry.type.name in ('tuple', 'str', 'bytes'):
-                        error(self.pos, "inheritance from PyVarObject types like '%s' is not currently supported"
-                              % base_class_entry.type.name)
-                    else:
-                        self.base_type = base_class_entry.type
-                if env.directives.get('freelist', 0) > 0:
-                    warning(self.pos, "freelists cannot be used on subtypes, only the base class can manage them", 1)
+                self.base_type = base_type
+            if env.directives.get('freelist', 0) > 0 and base_type != PyrexTypes.py_object_type:
+                warning(self.pos, "freelists cannot be used on subtypes, only the base class can manage them", 1)
 
         has_body = self.body is not None
         if has_body and self.base_type and not self.base_type.scope:
@@ -4752,6 +4718,31 @@ class CClassDefNode(ClassDefNode):
             else:
                 scope.implemented = 1
 
+        if len(self.bases.args) > 1:
+            if not has_body or self.in_pxd:
+                error(self.bases.args[1].pos, "Only declare first base in declaration.")
+            for other_base in self.bases.args[1:]:
+                if other_base.analyse_as_type(env):
+                    # TODO(robertwb): We may also want to enforce some checks
+                    # at runtime.
+                    error(other_base.pos, "Only one extension type base class allowed.")
+            if not self.scope.lookup("__dict__"):
+                #TODO(robertwb): See if this can be safely removed.
+                error(self.pos, "Extension types with multiple bases must have a __dict__ attribute")
+            self.entry.type.early_init = 0
+            from . import ExprNodes
+            self.type_init_args = ExprNodes.TupleNode(
+                self.pos,
+                args=[ExprNodes.IdentifierStringNode(self.pos, value=self.class_name),
+                      self.bases,
+                      ExprNodes.DictNode(self.pos, key_value_pairs=[])])
+        elif self.base_type:
+            self.entry.type.early_init = self.base_type.is_external or self.base_type.early_init
+            self.type_init_args = None
+        else:
+            self.entry.type.early_init = 1
+            self.type_init_args = None
+
         env.allocate_vtable_names(self.entry)
 
         for thunk in self.entry.type.defered_declarations:
@@ -4761,6 +4752,8 @@ class CClassDefNode(ClassDefNode):
         if self.body:
             scope = self.entry.type.scope
             self.body = self.body.analyse_expressions(scope)
+        if self.type_init_args:
+            self.type_init_args.analyse_expressions(env)
         return self
 
     def generate_function_definitions(self, env, code):
@@ -4774,8 +4767,160 @@ class CClassDefNode(ClassDefNode):
         code.mark_pos(self.pos)
         if self.body:
             self.body.generate_execution_code(code)
+        if not self.entry.type.early_init:
+            if self.type_init_args:
+                self.type_init_args.generate_evaluation_code(code)
+                bases = "PyTuple_GET_ITEM(%s, 1)" % self.type_init_args.result()
+                first_base = "((PyTypeObject*)PyTuple_GET_ITEM(%s, 0))" % bases
+                # Let Python do the base types compatibility checking.
+                trial_type = code.funcstate.allocate_temp(PyrexTypes.py_object_type, True)
+                code.putln("%s = PyType_Type.tp_new(&PyType_Type, %s, NULL);" % (
+                    trial_type, self.type_init_args.result()))
+                code.putln(code.error_goto_if_null(trial_type, self.pos))
+                code.put_gotref(trial_type)
+                code.putln("if (((PyTypeObject*) %s)->tp_base != %s) {" % (
+                    trial_type, first_base))
+                code.putln("PyErr_Format(PyExc_TypeError, \"best base '%s' must be equal to first base '%s'\",")
+                code.putln("             ((PyTypeObject*) %s)->tp_base->tp_name, %s->tp_name);" % (
+                           trial_type, first_base))
+                code.putln(code.error_goto(self.pos))
+                code.putln("}")
+                code.funcstate.release_temp(trial_type)
+                code.put_incref(bases, PyrexTypes.py_object_type)
+                code.put_giveref(bases)
+                code.putln("%s.tp_bases = %s;" % (self.entry.type.typeobj_cname, bases))
+                code.put_decref_clear(trial_type, PyrexTypes.py_object_type)
+                self.type_init_args.generate_disposal_code(code)
+                self.type_init_args.free_temps(code)
+
+            self.generate_type_ready_code(self.entry, code, True)
+
+    # Also called from ModuleNode for early init types.
+    @staticmethod
+    def generate_type_ready_code(entry, code, heap_type_bases=False):
+        # Generate a call to PyType_Ready for an extension
+        # type defined in this module.
+        type = entry.type
+        typeobj_cname = type.typeobj_cname
+        scope = type.scope
+        if not scope:  # could be None if there was an error
+            return
+        if entry.visibility != 'extern':
+            for slot in TypeSlots.slot_table:
+                slot.generate_dynamic_init_code(scope, code)
+            if heap_type_bases:
+
+                # As of https://bugs.python.org/issue22079
+                # PyType_Ready enforces that all bases of a non-heap type
+                # are non-heap.  We know this is the case for the solid base,
+                # but other bases may be heap allocated and are kept alive
+                # though the bases reference.
+                # Other than this check, this flag is unused in this method.
+                code.putln("#if PY_VERSION_HEX >= 0x03050000")
+                code.putln("%s.tp_flags |= Py_TPFLAGS_HEAPTYPE;" % typeobj_cname)
+                code.putln("#endif")
+            code.putln(
+                "if (PyType_Ready(&%s) < 0) %s" % (
+                    typeobj_cname,
+                    code.error_goto(entry.pos)))
+            if heap_type_bases:
+                code.putln("#if PY_VERSION_HEX >= 0x03050000")
+                code.putln("%s.tp_flags &= ~Py_TPFLAGS_HEAPTYPE;" % typeobj_cname)
+                code.putln("#endif")
+            # Don't inherit tp_print from builtin types, restoring the
+            # behavior of using tp_repr or tp_str instead.
+            code.putln("%s.tp_print = 0;" % typeobj_cname)
+            # Fix special method docstrings. This is a bit of a hack, but
+            # unless we let PyType_Ready create the slot wrappers we have
+            # a significant performance hit. (See trac #561.)
+            for func in entry.type.scope.pyfunc_entries:
+                is_buffer = func.name in ('__getbuffer__', '__releasebuffer__')
+                if (func.is_special and Options.docstrings and
+                        func.wrapperbase_cname and not is_buffer):
+                    slot = TypeSlots.method_name_to_slot[func.name]
+                    preprocessor_guard = slot.preprocessor_guard_code()
+                    if preprocessor_guard:
+                        code.putln(preprocessor_guard)
+                    code.putln('#if CYTHON_COMPILING_IN_CPYTHON')
+                    code.putln("{")
+                    code.putln(
+                        'PyObject *wrapper = PyObject_GetAttrString((PyObject *)&%s, "%s"); %s' % (
+                            typeobj_cname,
+                            func.name,
+                            code.error_goto_if_null('wrapper', entry.pos)))
+                    code.putln(
+                        "if (Py_TYPE(wrapper) == &PyWrapperDescr_Type) {")
+                    code.putln(
+                        "%s = *((PyWrapperDescrObject *)wrapper)->d_base;" % (
+                            func.wrapperbase_cname))
+                    code.putln(
+                        "%s.doc = %s;" % (func.wrapperbase_cname, func.doc_cname))
+                    code.putln(
+                        "((PyWrapperDescrObject *)wrapper)->d_base = &%s;" % (
+                            func.wrapperbase_cname))
+                    code.putln("}")
+                    code.putln("}")
+                    code.putln('#endif')
+                    if preprocessor_guard:
+                        code.putln('#endif')
+            if type.vtable_cname:
+                code.globalstate.use_utility_code(
+                    UtilityCode.load_cached('SetVTable', 'ImportExport.c'))
+                code.putln(
+                    "if (__Pyx_SetVtable(%s.tp_dict, %s) < 0) %s" % (
+                        typeobj_cname,
+                        type.vtabptr_cname,
+                        code.error_goto(entry.pos)))
+                if heap_type_bases:
+                    code.globalstate.use_utility_code(
+                        UtilityCode.load_cached('MergeVTables', 'ImportExport.c'))
+                    code.putln("if (__Pyx_MergeVtables(&%s) < 0) %s" % (
+                        typeobj_cname,
+                        code.error_goto(entry.pos)))
+            if not type.scope.is_internal and not type.scope.directives['internal']:
+                # scope.is_internal is set for types defined by
+                # Cython (such as closures), the 'internal'
+                # directive is set by users
+                code.putln(
+                    'if (PyObject_SetAttrString(%s, "%s", (PyObject *)&%s) < 0) %s' % (
+                        Naming.module_cname,
+                        scope.class_name,
+                        typeobj_cname,
+                        code.error_goto(entry.pos)))
+            weakref_entry = scope.lookup_here("__weakref__") if not scope.is_closure_class_scope else None
+            if weakref_entry:
+                if weakref_entry.type is py_object_type:
+                    tp_weaklistoffset = "%s.tp_weaklistoffset" % typeobj_cname
+                    if type.typedef_flag:
+                        objstruct = type.objstruct_cname
+                    else:
+                        objstruct = "struct %s" % type.objstruct_cname
+                    code.putln("if (%s == 0) %s = offsetof(%s, %s);" % (
+                        tp_weaklistoffset,
+                        tp_weaklistoffset,
+                        objstruct,
+                        weakref_entry.cname))
+                else:
+                    error(weakref_entry.pos, "__weakref__ slot must be of type 'object'")
+            if scope.lookup_here("__reduce_cython__") if not scope.is_closure_class_scope else None:
+                # Unfortunately, we cannot reliably detect whether a
+                # superclass defined __reduce__ at compile time, so we must
+                # do so at runtime.
+                code.globalstate.use_utility_code(
+                    UtilityCode.load_cached('SetupReduce', 'ExtensionTypes.c'))
+                code.putln('if (__Pyx_setup_reduce((PyObject*)&%s) < 0) %s' % (
+                              typeobj_cname,
+                              code.error_goto(entry.pos)))
+        # Generate code to initialise the typeptr of an extension
+        # type defined in this module to point to its type object.
+        if type.typeobj_cname:
+            code.putln(
+                "%s = &%s;" % (
+                    type.typeptr_cname, type.typeobj_cname))
 
     def annotate(self, code):
+        if self.type_init_args:
+            self.type_init_args.annotate(code)
         if self.body:
             self.body.annotate(code)
 

Cython/Compiler/Parsing.py

@@ -3435,19 +3435,15 @@ def p_c_class_definition(s, pos,  ctx):
         as_name = class_name
     objstruct_name = None
     typeobj_name = None
-    base_class_module = None
-    base_class_name = None
+    bases = None
     if s.sy == '(':
-        s.next()
-        base_class_path = [p_ident(s)]
-        while s.sy == '.':
-            s.next()
-            base_class_path.append(p_ident(s))
-        if s.sy == ',':
-            s.error("C class may only have one base class", fatal=False)
-        s.expect(')')
-        base_class_module = ".".join(base_class_path[:-1])
-        base_class_name = base_class_path[-1]
+        positional_args, keyword_args = p_call_parse_args(s, allow_genexp=False)
+        if keyword_args:
+            s.error("C classes cannot take keyword bases.")
+        bases, _ = p_call_build_packed_args(pos, positional_args, keyword_args)
+    if bases is None:
+        bases = ExprNodes.TupleNode(pos, args=[])
+
     if s.sy == '[':
         if ctx.visibility not in ('public', 'extern') and not ctx.api:
             error(s.position(), "Name options only allowed for 'public', 'api', or 'extern' C class")
@@ -3487,8 +3483,7 @@ def p_c_class_definition(s, pos,  ctx):
         module_name = ".".join(module_path),
         class_name = class_name,
         as_name = as_name,
-        base_class_module = base_class_module,
-        base_class_name = base_class_name,
+        bases = bases,
         objstruct_name = objstruct_name,
         typeobj_name = typeobj_name,
         in_pxd = ctx.level == 'module_pxd',

Cython/Compiler/PyrexTypes.py

@@ -1302,10 +1302,12 @@ class PyExtensionType(PyObjectType):
     #  vtabstruct_cname string           Name of C method table struct
     #  vtabptr_cname    string           Name of pointer to C method table
     #  vtable_cname     string           Name of C method table definition
+    #  early_init       boolean          Whether to initialize early (as opposed to during module execution).
     #  defered_declarations [thunk]      Used to declare class hierarchies in order
 
     is_extension_type = 1
     has_attributes = 1
+    early_init = 1
 
     objtypedef_cname = None
 

Cython/Utility/ImportExport.c

@@ -656,6 +656,67 @@ bad:
 }
 
 
+/////////////// MergeVTables.proto ///////////////
+//@requires: GetVTable
+
+static int __Pyx_MergeVtables(PyTypeObject *type); /*proto*/
+
+/////////////// MergeVTables ///////////////
+
+static int __Pyx_MergeVtables(PyTypeObject *type) {
+    int i;
+    void** base_vtables;
+    void* unknown = (void*)-1;
+    PyObject* bases = type->tp_bases;
+    int base_depth = 0;
+    {
+        PyTypeObject* base = type->tp_base;
+        while (base) {
+            base_depth += 1;
+            base = base->tp_base;
+        }
+    }
+    base_vtables = (void**) malloc(sizeof(void*) * (base_depth + 1));
+    base_vtables[0] = unknown;
+    // Could do MRO resolution of individual methods in the future, assuming
+    // compatible vtables, but for now simply require a common vtable base.
+    // Note that if the vtables of various bases are extended separately,
+    // resolution isn't possible and we must reject it just as when the
+    // instance struct is so extended.  (It would be good to also do this
+    // check when a multiple-base class is created in pure Python as well.)
+    for (i = 1; i < PyTuple_GET_SIZE(bases); i++) {
+        void* base_vtable = __Pyx_GetVtable(((PyTypeObject*)PyTuple_GET_ITEM(bases, i))->tp_dict);
+        if (base_vtable != NULL) {
+            int j;
+            PyTypeObject* base = type->tp_base;
+            for (j = 0; j < base_depth; j++) {
+                if (base_vtables[j] == unknown) {
+                    base_vtables[j] = __Pyx_GetVtable(base->tp_dict);
+                    base_vtables[j + 1] = unknown;
+                }
+                if (base_vtables[j] == base_vtable) {
+                    break;
+                } else if (base_vtables[j] == NULL) {
+                    // No more potential matching bases (with vtables).
+                    goto bad;
+                }
+                base = base->tp_base;
+            }
+        }
+    }
+    PyErr_Clear();
+    free(base_vtables);
+    return 0;
+bad:
+    PyErr_Format(
+        PyExc_TypeError,
+        "multiple bases have vtable conflict: '%s' and '%s'",
+        type->tp_base->tp_name, ((PyTypeObject*)PyTuple_GET_ITEM(bases, i))->tp_name);
+    free(base_vtables);
+    return -1;
+}
+
+
 /////////////// ImportNumPyArray.proto ///////////////
 
 static PyObject *__pyx_numpy_ndarray = NULL;

tests/errors/builtin_type_inheritance.pyx

@@ -12,7 +12,7 @@ cdef class MyStr(str): # only in Py2, but can't know that during compilation
     pass
 
 _ERRORS = """
-5:5: inheritance from PyVarObject types like 'tuple' is not currently supported
-8:5: inheritance from PyVarObject types like 'bytes' is not currently supported
-11:5: inheritance from PyVarObject types like 'str' is not currently supported
+5:19: inheritance from PyVarObject types like 'tuple' is not currently supported
+8:19: inheritance from PyVarObject types like 'bytes' is not currently supported
+11:17: inheritance from PyVarObject types like 'str' is not currently supported
 """

tests/errors/subtyping_final_class.pyx

@@ -10,5 +10,5 @@ cdef class SubType(FinalClass):
     pass
 
 _ERRORS = """
-9:5: Base class 'FinalClass' of type 'SubType' is final
+9:19: Base class 'FinalClass' of type 'SubType' is final
 """

tests/run/cdef_multiple_inheritance.pyx

+cdef class CBase(object):
+    cdef int a
+    cdef c_method(self):
+        return "CBase"
+    cpdef cpdef_method(self):
+        return "CBase"
+
+class PyBase(object):
+    def py_method(self):
+        return "PyBase"
+
+cdef class Both(CBase, PyBase):
+    cdef dict __dict__
+    """
+    >>> b = Both()
+    >>> b.py_method()
+    'PyBase'
+    >>> b.cp_method()
+    'Both'
+    >>> b.call_c_method()
+    'Both'
+
+    >>> isinstance(b, CBase)
+    True
+    >>> isinstance(b, PyBase)
+    True
+    """
+    cdef c_method(self):
+        return "Both"
+    cpdef cp_method(self):
+        return "Both"
+    def call_c_method(self):
+        return self.c_method()
+
+cdef class BothSub(Both):
+    """
+    >>> b = BothSub()
+    >>> b.py_method()
+    'PyBase'
+    >>> b.cp_method()
+    'Both'
+    >>> b.call_c_method()
+    'Both'
+    """
+    pass